Objectives were to characterize effects of average daily gain (ADG) on Warner-Bratzler shear force (WBSF) and characterize effects of ADG on postmortem proteolysis in steers. Thirty-six steers (initial body weight 271 ± 24 kg) were stratified by weight into 6 pens of 6 steers each. Steers were limit fed the same diet to obtain 3 different rates of gain (1.0, 1.5, and 1.85 kg/d). Steers were individually weighed every 2 weeks during the study period. Feed allocation was adjusted using the mean body weight of the pen, based on the NRC equation for net energy for gain. Steers were slaughtered in 3 independent slaughter groups after 151, 161, or 167 days on feed. During each slaughter event, the 2 heaviest animals from each pen were slaughtered. Four steers were removed from the study for having retained testicles. Temperature decline data were collected during carcass chilling starting 2 hrs postmortem. In addition, ultimate pH (UPH) of the longissimus muscle was collected. Individual grade and yield data were collected. Western blot samples and WBSF steaks were collected 24 hrs postmortem from the strip loin and randomly assigned to an aging time point (1, 7, 14, 21, 28, or 35 d). Western blot samples and shear force steaks were vacuum packaged and stored at 4 °C until assigned aging point, at which time western blot samples along with the corresponding shear steaks were frozen. Samples were also obtained from the strip loin for collagen quantification and sarcomere length determination. Sarcomere length was determined using laser diffraction. Soluble and insoluble collagen content was quantified using acid hydrolysis. Cook loss, percentage of weight loss during cooking, was calculated for each WBSF steak. Steer served as the experimental unit for each variable measured. All 32 steers were ranked by ADG and fifteen steers were selected for western blot analysis (5 steers with the greatest growth rate, 5 steers closest to the mean growth rate, and 5 steers with the slowest growth rate) were analyzed for desmin and troponin T degradation at 1 and 21 d postmortem aging time. As ADG increased by 1.0 kg/d, WBSF decreased by 1.42 kg in steaks aged for 1 d postmortem (1 d WBSF = 6.38 – (1.42*ADG, kg/d) Adj. R2 = 0.36). However, ADG did not account for any of the variation in WBSF at other postmortem aging points. A prediction model using a 4 variable equation accounted for 72% of the variation in 1 d WBSF (1 d WBSF = -25.28 + (4.30 * UPH) – (0.29 * extractable lipid, %) + (0.03 * skeletal maturity) + (0.20 * 1 d cook loss, %). Whereas, a 2 variable prediction equation only accounted for 47% of the variation in WBSF at 21 d postmortem (21 d WBSF = 0.39 + (0.10 * 21 d cook loss, %) + (0.09 * extractable lipid, %); Adj. R2 = 0.47). Degradation of the 37 kDa troponin T explained 27% of the variation observed in WBSF; however, degradation was not significant at 1 d postmortem. In conclusion, ADG accounted for 36% of the variation in WBSF at 1 d postmortem, but was not significant at other postmortem aging points. Multiple linear regression models were able to account for the variation in WBSF at 1 and 21 d postmortem.